"I think there's a kind of core, belief conviction element to this, which is that Xi has always sounded, since being elevated to power, like someone who feels like this has been his destiny," said Kerry Brown, an expert in Chinese politics at the University of Sydney.
"He's got all these powers and it seems to imply this kind of rather striking sense of destiny. The language he uses is increasingly grandiose and almost messianic."
The announcement of Xu's expulsion followed rumors that Xu, 71, had been detained from his sickbed in March. Some observers had thought Xu would be spared prosecution because of terminal cancer.
Experts said Xu was seen as an ally of Jiang, who still wields influence.
"Xu Caihou was often considered as Jiang's man and so probably this case indicates the further weakening of Jiang's influence and generally the weakening of what you may call `old man politics'," said Warren Sun, a Chinese leadership expert at Australia's Monash University. "He probably wants to signal more clearly the arrival of the Xi Jinping era."
Chronic corruption has fueled public frustration and Xi has warned it could threaten the party's grip on power.
In military affairs, party leaders worry pervasive graft is weakening the PLA's ability to fight.
The armed forces were ordered to give up most of their business interests more than a decade ago, but a secretive, authoritarian official culture has allowed bribery and other abuses to continue.
Previous Chinese leaders "had little control over the military and virtually let them have a free run and so corruption became very rampant," said Sun. "This is something that Xi Jinping's predecessors did not have the guts to deal with, but now we see him take action on something that's long overdue."
The purge of Xu eliminates an ally of one of Xi's rivals, former Chongqing party secretary Bo Xilai, who fell from power after his wife, Gu Kailai, was accused of killing her British business partner. Gu was convicted of murder and Bo was imprisoned last year on charges of corruption and abuse of power in a case that many saw as a result of party infighting.
Similarly, the party is widely believed to be investigating a retired senior leader, Zhou Yongkang, a former member of the party's apex of power who was seen as a Bo ally.
The party also on Monday had announced the expulsions of three senior officials believed linked to Zhou, which observers believe mean a public move against Zhou is inevitable.
"It's a life or death game within the party, and you will fall if you make any concessions," said Zhang Lifan, an independent political commentator in Beijing. "Thus you must defeat all the tigers within the party."
Lingering uncertainty about Zhou's fate might help Xi keep senior officials on edge.
"It creates this constant atmosphere of wariness and fear among the elite," said Brown of the University of Sydney. "There's this extraordinary manipulation of people not really knowing what's going on, and I think that's probably something that Xi is using."
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Gillian Wong has covered China for the AP since 2008.
AP writer Didi Tang contributed to this report.
